Home › Forum › Ask A Member › 1957 Big Twin 35hp questions oil, engine "Bucking" › Re: 1957 Big Twin 35hp questions oil, engine "Bucking"
Well, today’s oils are a lot better than what was available back in 1957, so I really don’t think 50:1 did any harm. And, I don’t think the bucking is related to the 50:1 mix.
If the engine seems to buck at high speeds as well as low speeds, my guess is the problem is ignition related. But, I have to ask how you know for sure that the engine is not jumping in and out of gear.
Is the engine electric start? If so, I would use a timing light to monitor ignition performance when the engine "bucks". This test is best done at dawn or dusk when the light is more visible. Clip the timing light to one spark plug wire at a time, you will probably need to remove the cover completely in order to connect the timing light and not pinch the lead. Have an assistant run the boat while the engine is bucking and watch the timing light. If the light is intermittent while the engine "bucks", then the problem is ignition related. Repeat this process with the other cylinder as well. Keep in mind that the timing light will be intermittent if you have a bad spark plug, so please to overlook the simple stuff. I suppose the vacuum switch could be causing ignition problems as well, but this probably would not be happening at higher speeds with the carb butterfly mostly open (least amount of vacuum to the switch).